An aqueous solution of Co(ClO4)2·6H2O is light pink in colour. Addition of conc. HCl results in an intense blue coloured solution due to the formation of a new species. The new species among the following is:
[Given: Atomic number of Co = 27]
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Cobalt(II) in aqueous solution appears pink due to \ce{[Co(H2O)6]^{2+}}, but turns deep blue upon the formation of tetrahedral \ce{[CoCl4]^{2-}} in concentrated HCl. Recognize this classic color change in transition metal chemistry.